Project Summary/Abstract Elderly patients currently comprise the majority of individuals undergoing inpatient surgery. Despite >90% of older adults living with one or more chronic health conditions, surgical intervention has become routine, as medical advancements have reduced peri-operative risk. While it has been a ground-breaking achievement to modify peri-operative risk at the individual level, it is equally important to do so at the systems level. This proposal will determine how surgeon volume (i.e., frequency of a given operation performed by a surgeon) and hospital volume (i.e., frequency of a given operation performed at a hospital) impact post-operative mortality of older adults. The findings will potentially have far-reaching implications for policymakers, hospitals, and patients, all of which seek for surgery to be performed under the safest possible circumstances. Previous work from nearly two decades ago studied the impact of hospital operative volume on mortality; other studies from the same era evaluated the association between surgeon operative volume and mortality. However, prior research was decontextualized in that it did not address the interrelatedness of surgeons and hospitals. As such, key questions remain unanswered. For example, to be credentialed, should surgeons at lower volume hospitals be required to exceed the same minimum volume standards as their counterparts at higher volume hospitals? In summary, is hospital volume only a sum of its affiliated surgeons? volumes ? or is there a protective spillover effect associated with a high-volume hospital context? This project will overcome the previous critical barriers and fill these knowledge gaps in two steps: (1) contextualizing the effect of surgeon and hospital volume on mortality after major vascular surgery by using contemporary multilevel techniques and (2) generalizing this approach to predict post-operative mortality by hospital and surgeon volumes for 11 major operations among older adults enrolled in Medicare. Ways in which differences in case-volume may perpetuate racial/ethnic and geographic disparities will additionally be examined. Preliminary results expand the existing research framework, wherein surgeons and hospitals have been treated as isolated ?silos.? Rather, a more complex, contextualized relationship is suggested in which hospital volume has a protective (?buffering?) effect on post-operative mortality, even with lower volume surgeons. In accordance with the National Institute on Aging?s goal of ?modifying organizational?behaviors in order to improve important health outcomes among members of population groups at older ages,? the results of these studies will inform optimal hospital and surgeon selection among older adults undergoing major operations. Under the close mentorship of faculty experts at Harvard T.H. Chan School of Public Health and Brigham and Women?s Hospital, the PI will gain expertise with advanced epidemiologic methods, a deep understanding of the analysis of Medicare data, and the preparation necessary to become a K-funded surgeon-scientist in the future.